U.S. patent application number 10/525739 was filed with the patent office on 2005-10-27 for multi-carrier communication method and multi-carrier communication method.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd. Invention is credited to Ebiko, Keisuke.
Application Number | 20050239488 10/525739 |
Document ID | / |
Family ID | 32211841 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050239488 |
Kind Code |
A1 |
Ebiko, Keisuke |
October 27, 2005 |
Multi-carrier communication method and multi-carrier communication
method
Abstract
A multi-carrier communication apparatus and a multi-carrier
communication method, wherein in a radio communication that
performs multi-antenna transmission, a transmission peak power is
suppressed without inducing nonlinear distortion and without
decreasing transmission efficiency. Based on control information
outputted from an exchange pattern decision section (190), a data
exchange section (120) exchanges data, which are arranged on
subcarriers of each group, between data streams in units of groups
of subcarriers. Power measurement sections (160-1 to n) each
measure powers of OFDM symbols in each data stream and compare them
with a predetermined threshold and as a result of comparison, when
the power of the OFDM symbol is greater than the predetermined
threshold, the measurement sections each output power measurement
results to an exchange pattern decision section (190). The exchange
pattern decision section (190) decides an exchange pattern for
exchanging data in the data stream of which the measured power is
greater than the predetermined threshold, and outputs it as control
information to the data exchange section (120).
Inventors: |
Ebiko, Keisuke;
(Yokosuka-shi, JP) |
Correspondence
Address: |
STEVENS DAVIS MILLER & MOSHER, LLP
1615 L STREET, NW
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd
|
Family ID: |
32211841 |
Appl. No.: |
10/525739 |
Filed: |
February 28, 2005 |
PCT Filed: |
October 30, 2003 |
PCT NO: |
PCT/JP03/13897 |
Current U.S.
Class: |
455/522 |
Current CPC
Class: |
H04L 5/0046 20130101;
H04L 27/2614 20130101; H04L 5/0048 20130101; H04L 5/0023 20130101;
H04L 5/006 20130101 |
Class at
Publication: |
455/522 |
International
Class: |
H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 1, 2002 |
JP |
2002-320158 |
Claims
1. A multi-carrier communication apparatus for simultaneously
transmitting a plurality of different data streams from a plurality
of antennas using the same carrier group, said apparatus
comprising: a determination section that determines whether a peak
power is occurred in at least one data stream, and an exchange
section that exchanges a part of data in said data stream for a
part of data in another data stream when it is determined that the
peak power is occurred.
2. The multi-carrier communication apparatus according to claim 1,
wherein said determination section comprises: a measurement section
that measures a power of each data stream, and a comparison section
that compares a measured power with a predetermined threshold, and
wherein said determination section determines a peak power is
occurred in a data stream of which the measured power is greater
than a predetermined threshold as a result of comparison.
3. The multi-carrier communication apparatus according to claim 1,
wherein said exchange section comprises: an exchange pattern
decision section that decides a pattern for exchanging a part of
data in each data stream in units of predetermined groups of
carriers, and a data exchange section that exchanges a part of data
in each data stream according to the decided exchange pattern.
4. The multi-carrier communication apparatus according to claim 3,
wherein said exchange pattern decision section decides a pattern
for exchanging data between groups having an equal frequency among
carrier groups.
5. The multi-carrier communication apparatus according to claim 3,
wherein said exchange pattern decision section decides a pattern
for exchanging data between groups having different frequencies
among carrier groups.
6. The multi-carrier communication apparatus according to claim 3,
wherein said data exchange section exchanges orthogonal pilot data
included in a part of data in each data stream.
7. The multi-carrier communication apparatus according to claim 3,
wherein said data exchange section does not exchange orthogonal
pilot data included in a part of data in each data stream.
8. The multi-carrier communication apparatus according to claim 1,
wherein said exchange section comprises a transmission section that
transmits exchange pattern information for communicating a pattern
for exchanging data to a communication opposite station.
9. The multi-carrier communication apparatus according to claim 8,
wherein said transmission section transmits exchange pattern
information using a particular carrier excluded from an object to
be exchanged.
10. The multi-carrier communication apparatus according to claim 1,
further comprising a formation section that forms different
directivity weights for each data stream, wherein when data are
exchanged by said exchange section, said formation section performs
an exchange of the directivity weights in response to an exchange
of the data.
11. The multi-carrier communication apparatus according to claim 1,
further comprising a production section that subjects transmit data
to coding so as to produce a plurality of different data streams
having a coding relation with each other.
12. The multi-carrier communication apparatus according to claim
11, wherein said production section subjects transmit data to block
coding at every predetermined block coding unit, and wherein said
exchange section performs an exchange of data using said block
coding unit as a minimum unit.
13. The multi-carrier communication apparatus according to claim
11, wherein said production section subjects transmit data to
convolution coding so as to produce a plurality of different data
streams.
14. The multi-carrier communication apparatus according to claim
11, wherein said production section subjects transmit data to
turbo-coding so as to produce a plurality of different data
streams.
15. A communication terminal apparatus having the multi-carrier
communication apparatus according to claim 1.
16. A base station apparatus having the multi-carrier communication
apparatus according to claim 1.
17. A multi-carrier communication method for simultaneously
transmitting a plurality of different data streams from a plurality
of antennas using the same carrier group, said method comprising
the steps of: determining whether a peak power is occurred in at
least one data stream, and exchanging a part of data in said data
stream for a part of data in another data stream when it is
determined that the peak power is occurred.
Description
TECHNICAL FIELD
[0001] The present invention relates to a multi-carrier
communication apparatus and a multi-carrier communication method
and in particular, it relates to a multi-carrier communication
apparatus and multi-carrier communication method for performing
multi-antenna transmission.
BACKGROUND ART
[0002] Recently, in mobile communications, a multi-carrier
modulation scheme and multi-antenna transmission have captured
attention in order to realize high-speed transmission through the
effective use of limited frequency resources. Further, studies have
been made to attain improvement in frequency utilization efficiency
by combining these two technologies (for example, refer to FIG. 4
in Japanese Unexamined patent publication No. 2002-44051).
[0003] For the multi-antenna transmission that transmits data using
a plurality of antennas, MIMO (Multi-Input Multi-Output) and STC
(Space-Time Coding) are known. In MIMO or STC, the same frequency
and the same spread code are used for different data streams, and
signals are transmitted from a plurality of transmitting antennas
at the same time. These signals are then superposed in a
propagation path and are received by a receiving set.
[0004] On the other hand, the multi-carrier modulation scheme is a
technology such that using a plurality of subcarriers in which the
transmission rate is suppressed to a level causing no frequency
selective fading, data are transmitted to thereby improve
transmission efficiency and as a result, high-speed transmission is
enabled. In particular, an OFDM (Orthogonal Frequency Division
Multiplex) modulation scheme is a scheme that is highest in
frequency utilization efficiency among the multi-carrier modulation
schemes because a plurality of subcarriers where data are arranged
are mutually orthogonalized. In addition, the OFDM modulation
scheme can be realized using a relatively simple hardware
configuration. Therefore, various studies have been made on the
OFDM modulation scheme.
[0005] As described above, in the multi-carrier modulation scheme
such as an OFDM modulation scheme, parallel transmission is carried
out using a plurality of subcarriers. At this time, when phases of
respective subcarriers are aligned, a remarkably large transmission
peak power is generated as compared with an average transmission
power. In such a case, although a transmission power amplifier
capable of maintaining the linearity of output over a wide dynamic
range must be used, in general, such an amplifier is low in
efficiency, which results in increase in the power consumption of
the apparatus.
[0006] Accordingly, for example, a method in which a transmission
power greater than a threshold is suppressed by a limiter to
thereby suppress the transmission peak power is employed in some
cases (for example, refer to FIG. 1 in Japanese Unexamined patent
publication No. 2002-44054). In addition, a transmission peak-power
suppressing method of using Partial Transmit Sequences called as
PTS is also known. In PTS, a plurality of groups of subcarriers are
formed, the subcarriers are subjected to inverse Fourier transform
for each group, and multiplied by different phase coefficients.
Then, the outputs of all the groups are added up to obtain a
signal, and such a sequence of phase coefficient that the peak
power of the obtained signal is minimized is selected. Further,
side information for communicating the selected sequence of the
phase coefficient to the receiving end is transmitted and at the
receiving end, reverse shift of the phase is performed based on the
side information, whereby data are demodulated (for example, refer
to Electronics Letters, Volume: 33, Issue: 5, 1997, "OFDM with
reduced peak-to-average power ratio by optimum combination of
partial transmit sequences", Muller, S. H.; Huber, J. B.).
[0007] However, for suppressing the transmission peak power in the
multi-carrier modulation, for example, when performing nonlinear
processing using a limiter, in general, there arise problems that
due to nonlinear distortion, interference among the subcarriers is
increased to result in deterioration of properties and unnecessary
out-of-band radiation is increased to result in interference with
out-of-band signals. Further, when using the PTS, there arises a
problem that the amount of side information different from
information to be normally transmitted is increased and as a
result, the transmission efficiency is lowered. These problems
similarly arise also when using a combination of the multi-antenna
transmission and the multi-carrier modulation scheme.
DISCLOSURE OF THE INVENTION
[0008] An object of the present invention is to provide a
multi-carrier communication apparatus and a multi-carrier
communication method, wherein in a radio communication that
performs multi-antenna transmission, a transmission peak power is
suppressed without inducing nonlinear distortion and without
decreasing transmission efficiency.
[0009] The present inventors have come up with the present
invention by taking into consideration the fact that in a
multi-carrier communication apparatus that performs multi-antenna
transmission, the content of data stream is different for each
transmitting antenna and a part of the data streams is exchanged
among the transmitting antennas, whereby transmission peak powers
of each antenna are varied.
[0010] That is, the essence of the present invention is to perform
transmission while exchanging a part of data streams among
transmitting antennas such that a transmission peak power reaches
equal to or lesser than a previously set threshold.
[0011] According to one aspect of the present invention, a
multi-carrier communication apparatus is an apparatus for
simultaneously transmitting a plurality of different data streams
from a plurality of antennas using the same carrier group, and the
apparatus adopts a structure including a determination section that
determines whether a peak power is occurred in at least one data
stream, and an exchange section that exchanges a part of data in
said data stream for a part of data in another data stream when it
is determined that the peak power is occurred.
[0012] According to another aspect of the present invention, a
multi-carrier communication method is a method for simultaneously
transmitting a plurality of different data streams from a plurality
of antennas using the same carrier group, and the method includes a
step of determining whether a peak power is occurred in at least
one data stream, and a step of exchanging a part of data in said
data stream for a part of data in another data stream when it is
determined that the peak power is occurred.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block diagram showing a configuration of a
transmitting multi-carrier communication apparatus according to a
first embodiment of the present invention;
[0014] FIG. 2 is a block diagram showing a configuration of a
receiving multi-carrier communication apparatus according to the
first embodiment;
[0015] FIG. 3 is a flow chart showing operations of a transmitting
multi-carrier communication apparatus according to the first
embodiment;
[0016] FIG. 4 is a diagram showing one example of data streams to
be transmitted from a plurality of transmitting antennas;
[0017] FIG. 5 is a diagram showing one example of a data exchange
in a transmitting multi-carrier communication apparatus according
to the first embodiment;
[0018] FIG. 6 is a block diagram showing a configuration of a
receiving multi-carrier communication apparatus according to a
second embodiment of the present invention;
[0019] FIG. 7 is a diagram showing one example of a data exchange
in a transmitting multi-carrier communication apparatus according
to the second embodiment;
[0020] FIG. 8 is a block diagram showing a configuration of a
transmitting multi-carrier communication apparatus according to a
third embodiment of the present invention;
[0021] FIG. 9 is a diagram explaining operations of a transmitting
multi-carrier communication apparatus according to the third
embodiment;
[0022] FIG. 10 is a block diagram showing a configuration of a
transmitting multi-carrier communication apparatus according to a
fourth embodiment of the present invention; and
[0023] FIG. 11 is a block diagram showing a configuration of a
receiving multi-carrier communication apparatus according to the
fourth embodiment of the present invention.
BEST MODE FOR CARRYING OUR THE INVENTION
[0024] With reference now to the attached drawings, embodiments of
the present invention will be explained in detail below. In the
following description, an OFDM modulation scheme is cited as one
example of a multi-carrier modulation scheme. Specifically, a case
is described where multi-carrier signals to be transmitted are OFDM
symbols.
First Embodiment
[0025] FIG. 1 is a block diagram showing a configuration of a
transmitting multi-carrier communication apparatus according to a
first embodiment of the present invention. The multi-carrier
communication apparatus shown in FIG. 1 has a demultiplexer 100,
S/P (Serial/Parallel) converters 110-1 to n (n is a natural number
of 2 or more), a data exchange section 120, IFFT (Inverse Fast
Fourier Transform) sections 130-1 to n, P/S (Parallel/Serial)
converters 140-1 to n, GI (Guard Interval) insertion sections 150-1
to n, power measurement sections 160-1 to n, radio transmission
sections 170-1 to n, transmitting antennas 180-1 to n and an
exchange pattern decision section 190. This multi-carrier
communication apparatus carries out MIMO transmission. In other
words, different data are simultaneously transmitted from
respective transmitting antennas 180-1 to n using the same
frequency and the same spread code.
[0026] The demultiplexer 100 divides transmit data into a plurality
of (n) data streams.
[0027] The S/P converters 110-1 to n S/P-convert respective data
streams to produce parallel data for each subcarrier.
[0028] Based on control information outputted from the exchange
pattern decision section 190, the data exchange section 120
exchanges a part of parallel data corresponding to each data stream
for a part of parallel data corresponding to another data stream.
At this time, the data exchange section 120 exchanges parallel data
of each data stream for that of another data stream in units of
groups formed by collecting a predetermined number of parallel
data. Since the parallel data each correspond to the subcarriers,
the group as a unit for data exchange is hereinafter referred to as
"a group of subcarriers" or simply referred to as "a group".
[0029] The IFFT sections 130-1 to n perform IFFT processing on the
parallel data outputted from the data exchange section 120 and
arrange the data on the subcarriers. Specifically, after the
parallel data are exchanged in units of groups of subcarriers, the
IFFT sections 130-1 to n perform IFFT processing on the parallel
data.
[0030] The P/S converters 140-1 to n P/S-convert the data in each
subcarrier outputted from the IFFT sections 130-1 to n to produce
OFDM symbols.
[0031] The GI insertion sections 150-1 to n insert guard intervals
into OFDM symbols in each data stream.
[0032] The power measurement sections 160-1 to n measure powers of
OFDM symbols in each data stream and compare them with a
predetermined threshold. Further, as a result of the comparison,
when the power of the OFDM symbol is equal to or lesser than the
predetermined threshold, the power measurement sections 160-1 to n
output the OFDM symbol to the radio transmission sections 170-1 to
n, and when the power of the OFDM symbol is greater than the
predetermined threshold, the power measurement sections 160-1 to n
output the power measurement results of each OFDM symbol to the
exchange pattern decision section 190.
[0033] The radio transmission sections 170-1 to n apply radio
transmission processing such as D/A conversion and up-conversion to
the OFDM symbols, and transmit the symbols from the transmitting
antennas 180-1 to n.
[0034] The exchange pattern decision section 190 decides an
exchange pattern for exchanging, in units of groups of subcarriers,
data in data streams of which the power measured by the power
measurement sections 160-1 to n is greater than the predetermined
threshold, and outputs the pattern to the data exchange section 120
as control information. Specific examples of the exchange pattern
are described later.
[0035] FIG. 2 is a block diagram showing a configuration of a
receiving multi-carrier communication apparatus according to the
first embodiment. The multi-carrier communication apparatus shown
in FIG. 2 has receiving antennas 200-1 to n, radio reception
sections 210-1 to n, GI removal sections 220-1 to n, S/P converters
230-1 to n, FFT (Fast Fourier Transform) sections 240-1 to n, a
data separator 250, demodulators 260-1 to n, P/S converters 270-1
to n, a multiplexer 280 and a propagation path estimation section
290.
[0036] The radio reception sections 210-1 to n receive OFDM symbols
from the receiving antennas 200-1 to n, and apply radio reception
processing such as down-conversion and A/D conversion to the
symbols.
[0037] The GI removal sections 220-1 to n remove guard intervals
from the OFDM symbols received from respective receiving antennas
200-1 to n.
[0038] The S/P converters 230-1 to n S/P-convert the OFDM symbols
in each data stream to produce parallel data for each
subcarrier.
[0039] The FFT sections 240-1 to n perform FFT-processing on the
parallel data in each data stream to produce data for each
subcarrier.
[0040] Based on the propagation path estimation results outputted
from the propagation path estimation section 290, the data
separator 250 separates the data for each subcarrier into the data
streams corresponding to the transmitting antennas 180-1 to n in
the transmitting multi-carrier communication apparatus.
[0041] Based on the propagation path estimation results outputted
from the propagation path estimation section 290, the demodulators
260-1 to n demodulate respective data streams.
[0042] The P/S converters 270-1 to n P/S-convert the demodulation
results outputted from the demodulators 260-1 to n to produce
serial data.
[0043] The multiplexer 280 multiplexes the serial data in each data
stream to obtain receive data.
[0044] Subsequently, operations of the multi-carrier communication
apparatus configured as described above are described by referring
to a flow chart shown in FIG. 3. The operations of the receiving
multi-carrier communication apparatus (FIG. 2) in the present
embodiment are the same as those of a conventional multi-carrier
communication apparatus and therefore, its description is
omitted.
[0045] First, transmit data are divided by the demultiplexer 100 to
produce n data streams. Respective data streams are each
S/P-converted by the S/P converters 110-1 to n to produce parallel
data for each data stream. The parallel data are inputted to the
IFFT sections 130-1 to n through the data exchange section 120, are
IFFT-processed by the IFFT sections 130-1 to n and then, the
resulting parallel data in each data stream are arranged on
subcarriers of which the frequencies are orthogonalized with each
other. More specifically, at the start of operations, the
IFFT-processing is carried out without performing an exchange of
data between the data streams.
[0046] Then, respective data streams after IFFT-processing are each
inputted to the P/S converters 140-1 to n and P/S-converted to
produce OFDM symbols.
[0047] Guard intervals are inserted into the OFDM symbols in each
data stream by the GI insertion sections 150-1 to n, and the powers
of the symbols are measured by the power measurement sections 160-1
to n (ST1000). The measured powers are compared with the
predetermined threshold (ST1100), and as a result of the
comparison, when the measured powers of all the data streams are
equal to or lesser than the predetermined threshold, the OFDM
symbols are subjected to radio transmission processing such as D/A
conversion and up-conversion by the radio transmission sections
170-1 to n and are transmitted through the transmitting antennas
180-1 to n (ST1200).
[0048] On the other hand, as a result of comparison of powers, when
a data stream of which the measured power exceeds the predetermined
threshold is present, the measured powers of each data stream are
communicated to the exchange pattern decision section 190. Then, by
the exchange pattern decision section 190, an exchange pattern is
decided in units of groups of subcarriers and outputted to the data
exchange section 120 as control information, in order to exchange a
part of the parallel data in a data stream of which the measured
power is greater than the predetermined threshold for a part of the
parallel data in another data stream. Then, an exchange of the
parallel data based on the control information is performed by the
data exchange section 120 (ST1300). In the multi-carrier
communication apparatus according to the present embodiment, the
content of the data in each data stream varies so as to carry out
MIMO transmission, and when a part of the parallel data is
exchanged as described above, a phase of the subcarrier where the
parallel data in each data stream are arranged is changed, namely,
the power is changed, so that a transmission peak power can be
suppressed.
[0049] After an exchange of parallel data, the data are again
IFFT-processed by the IFFT sections 130-1 to n, and P/S-converted
by the P/S converters 140-1 to n to produce OFDM symbols. Further,
guard intervals are inserted into the OFDM symbols by the GI
insertion sections 150-1 to n, the powers of the OFDM symbols are
measured by the power measurement sections 160-1 to n and then, the
measured powers are compared with the predetermined threshold.
Thereafter, in the same manner as in the above-described
operations, an exchange of parallel data is performed till powers
of all the OFDM symbols reach equal to or lesser than the
predetermined threshold, and when powers of all the OFDM symbols
reach equal to or lesser than the predetermined threshold (that is,
a transmission peak power is suppressed), respective OFDM symbols
are each transmitted through the transmitting antennas 180-1 to n
by the radio transmission sections 170-1 to n.
[0050] Subsequently, specific examples of the exchange pattern are
described by referring to FIGS. 4 and 5. For ease of description, a
case is herein used where the multi-carrier communication apparatus
has two transmitting antennas A and B; however, even when the
apparatus has three or more transmitting antennas, the parallel
data may be exchanged by an exchange pattern based on the same
concept.
[0051] FIG. 4 is a diagram schematically showing data streams
transmitted from each of the transmitting antennas A and B. In the
same figure, the horizontal axis indicates frequency and the
vertical axis indicates time.
[0052] From the transmitting antenna A, four symbols each are
transmitted by five subcarriers belonging to a group 300 and by
five subcarriers belonging to a group 310. Similarly, from the
transmitting antenna B, four symbols each are transmitted by five
subcarriers belonging to a group 320 and by five subcarriers
belonging to a group 330. The frequency of subcarriers belonging to
the group 300 is equal to that of subcarriers belonging to the
group 320, and the frequency of subcarriers belonging to the group
310 is equal to that of subcarriers belonging to the group 330.
P.sub.A and P.sub.B each indicate an orthogonal pilot symbol
periodically inserted.
[0053] In the present embodiment, a pattern for exchanging data
between the groups of subcarriers having the same frequency is used
as an exchange pattern. Accordingly, when a data stream of which
the measured power in the power measurement sections 160-1 to n is
greater than the predetermined threshold is present, for example, a
pattern for exchanging symbols of the group 310 for those of the
group 330 as shown in FIG. 5 is decided by the exchange pattern
decision section 190, this exchange pattern as the control
information is communicated to the data exchange section 120 and
then, the exchange of the data is actually performed.
[0054] At this time, since the orthogonal pilot symbols also are
exchanged as shown in FIG. 5, normal propagation path estimation is
performed by the propagation path estimation section 290 of the
receiving multi-carrier communication apparatus and based on the
results, separation of the data is performed by the data separator
250, so that the receiving multi-carrier communication apparatus
can correctly separate the data and demodulate them even when side
information on the exchange pattern of the data is not
obtained.
[0055] As described above, according to the present embodiment, a
part of data in a data stream of which the measured power is
greater than a predetermined threshold is exchanged for a part of
data including pilot symbols in another data stream arranged on a
sub-carrier having the same frequency as that of the data and
therefore, it is possible to prevent increase in interference among
sub-carriers without performing nonlinear processing, and to
suppress a transmission peak power without lowering transmission
efficiency while making side information unnecessary.
Second Embodiment
[0056] A second embodiment of the present invention is
characterized by introducing side information to increase the
number of exchange patterns and thereby, aiming at increasing an
effect of suppressing the transmission peak power.
[0057] A configuration of the transmitting multi-carrier
communication apparatus according to the second embodiment is the
same as that of the transmitting multi-carrier communication
apparatus (FIG. 1) according to the first embodiment and therefore,
its description is omitted.
[0058] FIG. 6 is a block diagram showing a configuration of the
receiving multi-carrier communication apparatus according to the
second embodiment. In the multi-carrier communication apparatus
shown in the same figure, the same sections as those in the
multi-carrier communication apparatus shown in FIG. 2 are assigned
the same symbols to omit the descriptions. The multi-carrier
communication apparatus shown in FIG. 6 has receiving antennas
200-1 to n, radio receiving sections 210-1 to n, GI removal
sections 220-1 to n, S/P converters 230-1 to n, FFT sections 240-1
to n, a data separator 250, a data exchange section 255,
demodulators 260-1 to n, P/S converters 270-1 to n, a multiplexer
280, a propagation path estimation section 290 and an exchange
pattern information extraction section 295.
[0059] Based on exchange pattern information transmitted as the
side information from the transmitting multi-carrier communication
apparatus, the data exchange section 255 exchanges the data, which
are arranged on subcarriers of each group, between the data
streams.
[0060] From the data streams, the exchange pattern information
extraction section 295 extracts the exchange pattern transmitted as
the side information from the transmitting multi-carrier
communication apparatus.
[0061] Subsequently, the operations of the multi-carrier
communication apparatus configured as described above are
described.
[0062] First, in the same manner as in the first embodiment,
transmit data are divided by the demultiplexer 100 to produce n
data streams. Respective data streams are S/P-converted by the S/P
converters 110-1 to n to produce parallel data for each data
stream. The parallel data are inputted to the IFFT sections 130-1
to n through the data exchange section 120, are IFFT-processed by
the IFFT sections 130-1 to n and then, the resulting parallel data
in each data stream are arranged on subcarriers of which the
frequencies are orthogonalized with each other. At this time, in
the present embodiment, an exclusive subcarrier is provided to
arrange exchange pattern information for the communication of an
exchange pattern to the receiving multi-carrier communication
apparatus.
[0063] Then, respective data streams after IFFT-processing are each
inputted to the P/S converters 140-1 to n and P/S-converted to
produce OFDM symbols.
[0064] Into the OFDM symbols of each data stream, guard intervals
are inserted by the GI insertion sections 150-1 to n, and the
powers of the symbols are measured by the power measurement
sections 160-1 to n. The measured powers are compared with the
predetermined threshold, and as a result of the comparison, when
the measured powers of all the data streams are equal to or lesser
than the predetermined threshold, the OFDM symbols are subjected to
radio transmission processing such as D/A conversion and
up-conversion by the radio transmission sections 170-1 to n and are
transmitted through the transmitting antennas 180-1 to n.
[0065] On the other hand, as a result of the comparison of powers,
when a data stream of which the measured power is greater than the
predetermined threshold is present, the measured powers of each
data stream are communicated to the exchange pattern decision
section 190. Then, by the exchange pattern decision section 190, an
exchange pattern is decided in units of groups of subcarriers and
outputted to the data exchange section 120 as control information,
in order to exchange a part of the parallel data in a data stream
of which the measured power is greater than the predetermined
threshold for a part of the parallel data in another data stream.
Then, an exchange of the parallel data based on the control
information is performed by the data exchange section 120.
[0066] At this time, exchange pattern information for the
communication of an exchange pattern decided by the exchange
pattern decision section 190 to the receiving multi-carrier
communication apparatus is arranged on an exclusive subcarrier. The
exchange pattern information may be MIMO transmitted from a
plurality of transmitting antennas or may be further transmitted
only from one transmitting antenna which is expected to correspond
to the best propagation path characteristics.
[0067] Thereafter, in the same manner as in the first embodiment,
an exchange of data is performed till powers of all the OFDM
symbols reach equal to or lesser than the predetermined threshold,
and when powers of all the OFDM symbols reach equal to or lesser
than the predetermined threshold (that is, a transmission peak
power is suppressed), respective OFDM symbols are transmitted
through the transmitting antennas 180-1 to n by the radio
transmission sections 170-1 to n.
[0068] Respective OFDM symbols transmitted are multiplexed on a
propagation path, received by respective receiving antennas 200-1
to n and subjected to radio reception processing such as
down-conversion and A/D conversion by the radio receiving sections
210-1 to n. From the OFDM symbols subjected to radio reception
processing, guard intervals are removed by the GI removal sections
220-1 to n, the symbols are then S/P-converted by the S/P
converters 230-1 to n and FFT-processed by the FFT sections 240-1
to-n. Thereafter, using the FFT processing results, propagation
path estimation is performed by the propagation path estimation
section 290, and the data in each subcarrier are separated by data
separator 250 so as to correspond to the data stream after the
group exchange at the transmitting end.
[0069] From each data stream obtained through the separation,
exchange pattern information is extracted by the exchange pattern
information extraction section 295. As described above, the
exchange pattern information may be included in a plurality of data
streams or may be further included only in one data stream.
[0070] Then, based on the extracted exchange pattern information,
an exchange of data is performed by the data exchange section 255
so that the data may correspond to the respective data streams
before the group exchange in the transmitting multi-carrier
communication apparatus. By doing so, the order of the data is made
equal to that of data before the group exchange in the transmitting
multi-carrier communication apparatus. Respective data streams
after the data exchange are demodulated by the demodulators 260-1
to n, P/S-converted by the P/S converters 270-1 to n and
multiplexed by the multiplexer 280, whereby receive data are
obtained.
[0071] Subsequently, specific examples of the exchange pattern are
described by referring to FIGS. 4 and 7. For ease of description, a
case is herein used where the multi-carrier communication apparatus
has two transmitting antennas A and B; however, even when the
apparatus has three or more transmitting antennas, the parallel
data may be exchanged by an exchange pattern based on the same
concept.
[0072] In the present embodiment, a part of the data in the data
stream shown in FIG. 4 can be exchanged to produce the data stream
as shown in FIG. 7. More specifically, an exchange pattern for
exchanging data between the groups of subcarriers having different
frequencies can be used. Accordingly, when a data stream of which
the measured power in the power measurement sections 160-1 to n is
greater than the predetermined threshold is present, for example, a
pattern for exchanging symbols of the group 310 for those of the
group 320 as shown in FIG. 7 is decided by the exchange pattern
decision section 190, this exchange pattern as the control
information is communicated to the data exchange section 120 and
then, the exchange of the data is actually performed.
[0073] At this time, as shown in FIG. 7, orthogonal pilot symbols
are not exchanged and fixedly assigned for each transmitting
antenna, so that the exchange of the data is enabled between the
groups of subcarriers having different frequencies. In addition,
exchange pattern information belonging to the group 400 and the
group 410 is arranged on exclusive subcarriers and transmitted.
[0074] Since the exchange pattern information of the present
embodiment is label information corresponding to the exchange
pattern, the amount of the side information is reduced and the
decreasing rate of transmission efficiency is small, as compared
with PTS where the sequence of the phase coefficient described in
the conventional art is transmitted as the side information.
[0075] In addition, the orthogonal pilot symbols are excluded from
an object to be exchanged and therefore, a propagation path
estimated value between groups can be subjected to interpolation
processing in the propagation path estimation section 290 at the
receiving end.
[0076] As described above, according to the present embodiment, a
part of data in a data stream of which the measured power is
greater than a predetermined threshold is exchanged for a part of
data other than the pilot symbols in another data stream and
therefore, it is possible to prevent increase in interference among
sub-carriers without performing nonlinear processing, and to
perform an exchange of data is more freely, so that a transmission
peak power can be further suppressed.
Third Embodiment
[0077] A third embodiment of the present invention is characterized
by performing directional transmission using different transmission
weights for each data stream to remove a spatial correlation
between a transmitting antenna and a receiving antenna.
[0078] FIG. 8 is a block diagram showing a configuration of the
transmitting multi-carrier communication apparatus according to the
third embodiment. In the multi-carrier communication apparatus
shown in the same figure, the same sections as those in the
multi-carrier communication apparatus shown in FIG. 1 are assigned
the same symbols to omit the descriptions. The multi-carrier
communication apparatus shown in FIG. 8 has a demultiplexer 100,
S/P converters 110-1 to n, a data exchange section 120, IFFT
sections 130-1 to n, P/S converters 140-1 to n, GI insertion
sections 150-1 to n, power measurement sections 160-1 to n, radio
transmission sections 170-1 to n, transmitting antennas 180-1 to n,
an exchange pattern decision section 190 and a directivity weight
formation section 500.
[0079] The directivity weight formation section 500 performs
weighting on respective data streams using different directivity
weights.
[0080] A configuration of the receiving multi-carrier communication
apparatus according to the third embodiment is the same as that of
the receiving multi-carrier communication apparatus (FIG. 2)
according to the first embodiment and therefore, its description is
omitted.
[0081] Subsequently, operations of the multi-carrier communication
apparatus configured as described above are described. The
operations of the receiving multi-carrier communication apparatus
(FIG. 2) in the present embodiment are the same as that of a
conventional multi-carrier communication apparatus and therefore,
its description is omitted.
[0082] First, in the same manner as in the first embodiment,
transmit data are divided by the demultiplexer 100 to produce n
data streams. Respective data streams are each S/P-converted by the
S/P converters 110-1 to n to produce parallel data for each data
stream. The parallel data are inputted to the IFFT sections 130-1
to n through the data exchange section 120, are IFFT-processed by
the IFFT sections 130-1 to n and then, the resulting parallel data
in each data stream are arranged on subcarriers of which the
frequencies are orthogonalized with each other.
[0083] Then, respective data streams IFFT-processed are inputted to
the directivity weight formation section 500 and weighed using
different directivity weights for each data stream. Respective data
streams weighed are inputted to the P/S converters 140-1 to n and
P/S-converted to produce OFDM symbols.
[0084] Guard intervals are inserted into the OFDM symbols in each
data stream by the GI insertion sections 150-1 to n, and the powers
of the symbols are measured by the power measurement sections 160-1
to n. The measured powers are compared with the predetermined
threshold, and as a result of the comparison, when the measured
powers of all the data streams are equal to or lesser than the
predetermined threshold, the OFDM symbols are subjected to radio
transmission processing such as D/A conversion and up-conversion by
the radio transmission sections 170-1 to n and are directionally
transmitted through the transmitting antennas 180-1 to n.
[0085] At this time, since each data stream is weighed by the
directivity weight, for example, when the apparatus has four
transmitting antennas (in the case of n=4), four data streams 1 to
4 are each transmitted in different directivities as shown in FIG.
9. In other words, the transmitting antenna and the data stream do
not have one-to-one correspondence relation but the correspondence
relation between the directivity and the data stream varies due to
an exchange of the data by the data exchange section 120. As a
result, since the spatial correlation between the transmitting
antenna and the receiving antenna in each data stream is removed,
the separation accuracy of data in the receiving multi-carrier
communication apparatus can be improved.
[0086] On the other hand, as a result of the comparison of powers,
when a data stream of which the measured power is greater than the
predetermined threshold is present, the measured powers of each
data stream are communicated to the exchange pattern decision
section 190. Then, by the exchange pattern decision section 190, an
exchange pattern is decided in units of groups of subcarriers and
outputted to the data exchange section 120 as control information,
in order to exchange a part of the parallel data in a data stream
of which the measured power is greater than the predetermined
threshold for a part of the parallel data in another data stream.
Then, an exchange of the parallel data based on the control
information is performed by the data exchange section 120.
[0087] Thereafter, in the same manner as in the first embodiment,
an exchange of data is performed till powers of all the OFDM
symbols reach equal to or lesser than the predetermined threshold,
and when powers of all the OFDM symbols reach equal to or lesser
than the predetermined threshold (that is, a transmission peak
power is suppressed), respective OFDM symbols are directionally
transmitted through the transmitting antennas 180-1 to n by the
radio transmission sections 170-1 to n.
[0088] As described above, according to the present embodiment, a
part of data in a data stream of which the measured power is
greater than a predetermined threshold is exchanged for a part of
data in another data stream arranged on a sub-carrier having the
same frequency as that of the data and therefore, it is possible to
prevent increase in interference among sub-carriers without
performing nonlinear processing, and to suppress a transmission
peak power without lowering transmission efficiency while making
side information unnecessary. Further, respective data streams are
weighed using different directivity weights, so that a correlation
between the propagation environments can be removed and as a
result, the separation accuracy of data at the receiving end can be
improved.
[0089] In the present embodiment, not only a correspondence
relation between the data stream and the directivity weight is
changed but also the directivity weight itself for use in each data
stream may be further changed.
Fourth Embodiment
[0090] A fourth embodiment of the present invention is
characterized in that a plurality of data streams being produced by
STC (Space-Time Coding) or by SFC (Space-Frequency Coding) and
having a coding relation with each other are subjected to
multi-carrier modulation.
[0091] FIG. 10 is a block diagram showing a configuration of a
transmitting multi-carrier communication apparatus according to the
fourth embodiment. In the multi-carrier communication apparatus
shown in the same figure, the same sections as those in the
multi-carrier communication apparatus shown in FIG. 1 are assigned
the same symbols to omit the descriptions. The multi-carrier
communication apparatus shown in FIG. 10 has S/P converters 110-1
to n, a data exchange section 120, IFFT sections 130-1 to n, P/S
converters 140-1 to n, GI insertion sections 150-1 to n, power
measurement sections 160-1 to n, radio transmission sections 170-1
to n, transmitting antennas 180-1 to n, an exchange pattern
decision section 190, and a space-time coder 600.
[0092] The space-time coder 600 subjects transmit data to
Space-Time Coding so as to produce data streams having a coding
relation with each other (namely, for example, information bits and
redundant bits to the information bits).
[0093] FIG. 11 is a block diagram showing a configuration of a
receiving multi-carrier communication apparatus according to the
fourth embodiment. In the multi-carrier communication apparatus
shown in the same figure, the same sections as those in the
multi-carrier communication apparatus shown in FIG. 2 are assigned
the same symbols to omit the descriptions. The multi-carrier
communication apparatus shown in FIG. 11 has receiving antennas
200-1 to n, radio reception sections 210-1 to n, GI removal
sections 220-1 to n, S/P converters 230-1 to n, FFT sections 240-1
to n, a propagation path estimation section 290, a space-time
decoder 700, and a P/S converter 710.
[0094] Based on the propagation path estimation results outputted
from the propagation path estimation section 290, the space-time
decoder 700 performs Space-Time decoding of each data stream and
outputs the decoded results.
[0095] The P/S converter 710 P/S-converts the decoded results to
produce receive data.
[0096] Next, operations of the multi-carrier communication
apparatus configured as described above are described.
[0097] First, transmit data are subjected to Space-Time Coding by
the space-time coder 600 to produce n data streams having a coding
relation with each other. Respective data streams are each
S/P-converted by the S/P converters 110-1 to n to produce parallel
data for each data stream. The parallel data are inputted to the
IFFT sections 130-1 to n through the data exchange section 120, are
IFFT-processed by the IFFT sections 130-1 to n and then, the
resulting parallel data in each data stream are arranged on
sub-carriers of which the frequencies are orthogonalized with each
other.
[0098] Then, respective data streams IFFT-processed are inputted to
the P/S converters 140-1 to n and P/S converted to produce OFDM
symbols.
[0099] Guard intervals are inserted into the OFDM symbols in each
data stream by the GI insertion sections 150-1 to n, and the powers
of the symbols are measured by the power measurement sections 160-1
to n. The measured powers are compared with the predetermined
threshold, and as a result of the comparison, when the measured
powers of all the data streams are equal to or lesser than the
predetermined threshold, the OFDM symbols are subjected to radio
transmission processing such as D/A conversion and up-conversion by
the radio transmission sections 170-1 to n and are transmitted
through the transmitting antennas 180-1 to n.
[0100] On the other hand, as a result of the comparison of powers,
when a data stream of which the measured power is greater than the
predetermined threshold is present, the measured powers of each
data stream are communicated to the exchange pattern decision
section 190. Then, by the exchange pattern decision section 190, an
exchange pattern is decided in units of groups of subcarriers and
outputted to the data exchange section 120 as control information,
in order to exchange a part of the parallel data in a data stream
of which the measured power is greater than the predetermined
threshold for a part of the parallel data in another data stream.
Then, an exchange of the parallel data based on the control
information is performed by the data exchange section 120.
[0101] At this time, an exchange of data is performed only between
groups of subcarriers having the same frequency as shown in FIG. 5
(first embodiment) because in STC or SFC, separation of data
streams is performed assuming that respective data streams have a
coding relation with each other. That is, an exchange of data is
performed such that respective symbols transmitted at the same time
and at the same frequency always have a coding relation with each
other.
[0102] In particular, when a block coding such as STTD (Space-Time
coded Transmit Diversity) is employed as a coding method in the
space-time coder 600, the space-time decoder 700 performs block
decoding processing assuming that propagation path characteristics
of symbols continuing in terms of time and frequency scarcely vary.
Therefore, when the block coding unit in the space-time coder 600
extends between groups for data exchange in the data exchange
section 120, the assumption on the propagation path characteristics
is not realized due to an exchange of data, as a result, the block
decoding processing is not correctly performed. For this reason, a
group for data exchange is formed using a block coding unit as a
minimum unit.
[0103] Thereafter, in the same manner as in the first embodiment,
an exchange of data is performed till powers of all the OFDM
symbols reach equal to or lesser than the predetermined threshold,
and when powers of all the OFDM symbols reach equal to or lesser
than the predetermined threshold (that is, a transmission peak
power is suppressed), respective OFDM symbols are transmitted
through the transmitting antennas 180-1 to n by the radio
transmission sections 170-1 to n.
[0104] Respective OFDM symbols transmitted are multiplexed on a
propagation path, received by respective receiving antennas 200-1
to n and subjected to radio reception processing such as
down-conversion and A/D conversion by the radio receiving sections
210-1 to n. From the OFDM symbols subjected to radio reception
processing, guard intervals are removed by the GI removal sections
220-1 to n, the symbols are then S/P-converted by the S/P
converters 230-1 to n and FFT-processed by the FFT sections 240-1
to n. Thereafter, using the FFT processing results, propagation
path estimation is performed by the propagation path estimation
section 290, and decoding processing corresponding to the
Space-Time Coding at the transmitting end is performed by the
space-time decoder 700.
[0105] Then, the decoded results are P/S-converted by the P/S
converter 710, whereby receive data can be obtained.
[0106] As described above, according to the present embodiment, a
part of data in a data stream of which the measured power is
greater than a predetermined threshold is exchanged with a part of
data in another data stream arranged on a sub-carrier having the
same frequency as that of the data and therefore, even when a
multi-antenna transmission such as STC or SFC is performed, it is
possible to prevent increase in interference among sub-carriers and
to suppress a transmission peak power without lowering transmission
efficiency while making side information unnecessary.
[0107] When a function of applying spread coding to data in the
frequency axis direction is added to each of the embodiments, an
exchange pattern causing no collapse of orthogonality between
diffusion chips is used, whereby the same effects can be
obtained.
[0108] As described above, according to the present invention, in
the radio communication that performs multi-antenna transmission,
the transmission peak power can be suppressed without inducing
nonlinear distortion and without decreasing transmission
efficiency.
[0109] This application is based on Japanese Patent Application No.
2002-320158 filed on Nov. 1, 2002, entire content of which is
incorporated by reference herein.
INDUSTRIAL APPLICABILITY
[0110] The present invention can be applied to a multi-carrier
communication apparatus and multi-carrier communication method for
performing multi-antenna transmission.
[0111] FIG. 1
[0112] TRANSMIT DATA
[0113] 100 DEMULTIPLEXER
[0114] 110-1 to n S/P CONVERTER
[0115] 120 DATA EXCHANGE SECTION
[0116] 130-1 to n IFFT SECTION
[0117] 140-1 to n P/S CONVERTER
[0118] 150-1 to n GI INSERTION SECTION
[0119] 160-1 to n POWER MEASUREMENT SECTION
[0120] 170-1 to n RADIO TRANSMISSION SECTION
[0121] 190 EXCHANGE PATTERN DECISION SECTION
[0122] FIG.2
[0123] 210-1 to n RADIO RECEPTION SECTION
[0124] 220-1 to n GI REMOVAL SECTION
[0125] 230-1 to n S/P CONVERTER
[0126] 240-1 to n FFT SECTION
[0127] 250 DATA SEPARATOR
[0128] 260-1 to n DEMODULATOR
[0129] 270-1 P/S CONVERTER
[0130] 280 MULTIPLEXER
[0131] 290 PROPAGATION PATH ESTIMATION SECTION
[0132] RECEIVE DATA
[0133] FIG.3
[0134] START
[0135] ST1000 MEASURE TRANSMISSION POWER
[0136] ST1100 IS TRANSMISSION POWER EQUAL TO OR LESSER THAN
THRESHOLD?
[0137] ST1200 DATA TRANSMISSION
[0138] ST1300 EXCHANGE PART OF DATA
[0139] END
[0140] FIG. 4
[0141] TIME
[0142] TRANSMITTING ANTENNA A(B)
[0143] ONE SYMBOL
[0144] ONE SUBCARRIER
[0145] FREQUENCY
[0146] FIG. 5
[0147] TIME
[0148] TRANSMITTING ANTENNA A(B)
[0149] ONE SYMBOL
[0150] ONE SUBCARRIER
[0151] FREQUENCY
[0152] FIG. 6
[0153] 210-1 to n RADIO RECEPTION SECTION
[0154] 220-1 to n GI REMOVAL SECTION
[0155] 230-1 to n S/P CONVERTER
[0156] 240-1 to n FFT SECTION
[0157] 250 DATA SEPARATOR
[0158] 255 DATA EXCHANGE SECTION
[0159] 260-1 to n DEMODULATOR
[0160] 270-1 to n P/S CONVERTER
[0161] 280 MULTIPLEXER
[0162] 290 PROPAGATION PATH ESTIMATION SECTION
[0163] 295 EXCHANGE PATTERN INFORMATION EXTRACTION SECTION
[0164] RECEIVE DATA
[0165] FIG. 7
[0166] TIME
[0167] TRANSMITTING ANTENNA A(B)
[0168] ONE SYMBOL
[0169] ONE SUBCARRIER
[0170] FREQUENCY
[0171] FIG. 8
[0172] TRANSMIT DATA
[0173] 100 DEMULTIPLEXER
[0174] 110-1 to n S/P CONVERTER
[0175] 120 DATA EXCHANGE SECTION
[0176] 130-1 to n IFFT SECTION
[0177] 140-1 to n P/S CONVERTER
[0178] 150-1 to n GI INSERTION SECTION
[0179] 160-1 to n POWER MEASUREMENT SECTION
[0180] 170-1 to n RADIO TRANSMISSION SECTION
[0181] 190 EXCHANGE PATTERN DECISION SECTION
[0182] 500 DIRECTIVITY WEIGHT FORMATION SECTION
[0183] FIG. 9
[0184] DIRECTIVITY OF DATA STREAM 1 (2, 3 and 4)
[0185] MULTI-CARRIER COMMUNICATION APPARATUS
[0186] FIG. 10
[0187] TRANSMIT DATA
[0188] 110-1 to n S/P CONVERTER
[0189] 120 DATA EXCHANGE SECTION
[0190] 130-1 to n IFFT SECTION
[0191] 140-1 to n P/S CONVERTER
[0192] 150-1 to n GI INSERTION SECTION
[0193] 160-1 to n POWER MEASUREMENT SECTION
[0194] 170-1 to n RADIO TRANSMISSION SECTION
[0195] 190 EXCHANGE PATTERN DECISION SECTION
[0196] 600 SPACE-TIME CODER
[0197] FIG. 11
[0198] 210-1 to n RADIO RECEPTION SECTION
[0199] 220-1 to n GI REMOVAL SECTION
[0200] 230-1 to n S/P CONVERTER
[0201] 240-1 to n FFT SECTION
[0202] 290 PROPAGATION PATH ESTIMATION SECTION
[0203] 700 SPACE-TIME DECODER
[0204] 710 P/S CONVERTER
[0205] RECEIVE DATA
* * * * *